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XT2YZ

2008 YZ450 valvetrain issue

16 posts in this topic

I have a stock 2008 YZ450 with 26 hours on it. I use Amsoil MCF and change it every five hours. I have not been into the motor. Recently I have been getting some loud ticking, almost a clacking, out of the top end. It comes and goes, almost like something is stuck and then frees up. Yesterday (Sunday) I started it and there was no noise. I let it warm up for a minute. As soon as I gave it some gas I got the sound of really loose valves. If I rev the motor just a few thousand rpms it fades, then I hear it again at idle. I went out for practice and when I came back, no more noise. No more noise for the rest of the day. It did the same thing last weekend but I also rode Saturday with no occurrence.

I am hoping someone might shed some light on this before I go digging. Any input is appreciated.

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Normally, most of the noise in a YZ450 is generated in the primary drive gears and transmission, and not so much in the valve train. Having the noise diminish by raising the engine speed higher than idle supports this, as it is the fact that the engine does not truly run at a steady speed at or near idle that causes all the rattling. However, the valve train could be involved.

Start by checking the clearances. Then, while you have it open, do a quick inspection of the tensioner and chain:

  • Position the engine at TDC with the cam lobes pointing up and out, not down and in.
  • Remove the center cap screw from the tensioner (see page 4-18 of the manual).
  • Insert a small screwdriver into the slot in the tensioner under where the center screw was and rotate the tensioner drive shaft clockwise as if tightening it. There will be spring tension resisting you, but it should move freely, and when released, it should return smoothly to it's original position.
  • Wind the tensioner in a way and hold it. Push downward on the cam chain between the two cams to create some slack, and check that the accessible links seem free and do not bind or kink.

If you have any doubts regarding the tensioner, you can remove it and inspect it further, or just replace it.

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My shop just did the valve inspection on my '08 and found the cam chain needed to be replaced...links were binding up all over the place.

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My shop just did the valve inspection on my '08 and found the cam chain needed to be replaced...links were binding up all over the place.
There have been a few like that in the '08 model year.

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There have been a few like that in the '08 model year.

I'm glad I recently replaced my camchain after reading these '08 comments:-o

xt2yz, hope that clears up your "clanking" problems.

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Start by checking the clearances. Then, while you have it open, do a quick inspection of the tensioner and chain:

  • Position the engine at TDC with the cam lobes pointing up and out, not down and in.
  • Remove the center cap screw from the tensioner (see page 4-18 of the manual).
  • Insert a small screwdriver into the slot in the tensioner under where the center screw was and rotate the tensioner drive shaft clockwise as if tightening it. There will be spring tension resisting you, but it should move freely, and when released, it should return smoothly to it's original position.
  • Wind the tensioner in a way and hold it. Push downward on the cam chain between the two cams to create some slack, and check that the accessible links seem free and do not bind or kink.

If you have any doubts regarding the tensioner, you can remove it and inspect it further, or just replace it.

So, the valves are all in spec. The cam chain seems fine as well. I removed the chain tensioner. When I turn it in and release, it comes back out smoothly. Except for when I turn it all the way in. Then it sticks. It will not let loose and return without some help. Does the tensioner, under normal operation, ever max out like that? If so, it is definetly not working correctly and may be the culprit. Either way, it is highly suspect and I'll be replacing it.

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So, the valves are all in spec. The cam chain seems fine as well. I removed the chain tensioner. When I turn it in and release, it comes back out smoothly. Except for when I turn it all the way in. Then it sticks. It will not let loose and return without some help. Does the tensioner, under normal operation, ever max out like that? If so, it is definetly not working correctly and may be the culprit. Either way, it is highly suspect and I'll be replacing it.

Your tensioner sounds fine. They all stick when backed off all the way, this way you can reinstall it without having to hold it backed off the whole time. In operation the tensioner should never be near that far in.

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Your tensioner sounds fine. They all stick when backed off all the way, this way you can reinstall it without having to hold it backed off the whole time. In operation the tensioner should never be near that far in.

OK, perhaps I was a bit hasty when I inspected the chain. After reading your post I went back out to the garage and the chain is now the "highly suspect" component. I am having trouble locating a specific link or links that are binding but when I rotate it there is a spot where the chain won't seat properly in the cam sprocket.

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Recently I have been getting some loud ticking, almost a clacking, out of the top end. It comes and goes,

Sounds like my 08. Time to check my chain. Thanks for the timely post.:doh:

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What type of flywheel puller will I need for replacing the chain. I mean, is it specific to the bike?

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Yes, but it's the same one as used for the CRF450, so you should have no trouble finding one.

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What type of flywheel puller will I need for replacing the chain. I mean, is it specific to the bike?

I just bought and used this one: http://www.rockymountainatvmc.com/productDetail.do?navType=type&navTitle=Engine&webCatId=17&webTypeId=203&prodFamilyId=17329&stockId=143963#vehicleSelect

Read this also http://www.thumpertalk.com/forum/showthread.php?t=568177

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Well, replaced the cam chain. It had two links that were binding. Unfortunately, this did not solve my problem. My engine is still making the same noise. Any other ideas? The more I listen to it, I'm starting to think it sounds like the piston. I have ridden the bike four or five times since I first noticed it. Sometimes it doesn't make the noise at all. Other times, it will just sort of come and go. It has always run fine and never given me any sign of a problem besides the noise.

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Something else I noticed. After just an hour of use, my oil is coming out a dirty, grey color.

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